The present invention relates in general to tube and pipe manufacturing techniques, and in particular to a new and useful method of making a tube which has an integral joint formed by an enlarged end of the tube. A tube which initially has a uniform outside diameter, wall thickness and inside diameter, can be provided with one or two integral joint ends by heating the end or ends of the tube and hot upsetting that end to increase the outside diameter and the wall thickness, and to decrease the inside diameter, at the end of the tube. This upset and enlarged end can subsequently be machined to form male or female threads.
Before machining the upset ends of such a tube, it is known to heat treat the entire tube to obtain a desired strength level. It is also known to initially manufacture the tube along with its upset ends so that it has its nominal finished size.
This technique however is not applicable for tubes made of materials that develop strength by cold working. Such materials must be cold worked at least to a minimum extent to obtain a required strength. Uniform cold working is desired to obtain uniform properties. It has been considered impractical to use such materials to form tubes having upset ends because cold upsetting is an impractical technique for forming these ends. This is because the forces are too high to upset the ends with a small number of blows or hits and the number of hits is too high if lower forces are used. Even if these difficulties were overcome however it is not possible to control the amount and uniformity of cold working along the entire length of the tube. While the ends of such a tube might be strengthened by the cold upsetting action, the intermediate length of the tube would not be strengthened.